1 Field of the Invention
The present invention relates to an electrostatic toner useful for either laser printer and/or plain paper copier machines.
2 Description of the Background
Developing methods and associated toners for use in electrostatic development in electrophotography are known, and include for example, dual-component developing methods, which use as image-forming particles and larger carrier particles, and mono-component developing methods, which use a toner comprising only magnetic or non-magnetic image-forming particles, or with a small amount of additive particles. Such developing methods are described in Kirk-Othmer, Encyclopedia of Chemical Technology, 4.sup.th ed., 9:261-275 (1994).
An image forming apparatus utilizing an electrophotographic method with toner is well known. In the image forming apparatus utilizing the electrophotographic method, images are generally formed onto a sheet of copy paper through the following processes.
After uniformly charging a photoconductor that serves as an image-holding body, images are exposed onto the surface of the charged photoconductor. Attenuating electrostatic charges during the exposure of light forms a latent image. Then the electrostatic latent images are visualized by developing with toner to form a toner image. The toner images are transferred onto a sheet of copy paper.
A laser printer, a LED printer and the like have been developed in recent years, wherein the image scanning part and the image output part are separated from each other. In these apparatuses, a reversed development method, i.e., the toner is made to adhere to the portions where the charge at the portions of the image exposure has been attenuated, is adopted (in contrast to the above, where toner is made to adhere to the portions where charge still remains in the normal development method).
Transfer of the image-forming particles to the non-image areas causes an undesirable phenomenon in view of image quality as a so-called "ghosting," in which are formed"memory images" normally formed during contact with the magnetic sleeve roller which is usually part of the toner cartridge assembly. Ghosting can be described as developed image-forming patterns on a latent image-retaining member which are electrostatically transferred to a transfer material such as paper. These images become visual and the image formed can either be lighter than the background formed by toner deposition or darker than the background formed by toner deposition. In instances where the "ghost" image is lighter than the background, this phenomena is known as "negative ghosting." In instances where the "ghost" image is darker than the background, this phenomenon is known as "positive ghosting."
If the ghost image (negative or positive type) is repeated several times on the transfer material (paper), this can usually be attributed to the photoconductor drum allowing a "memory defect" to occur. If, however, the ghost image appears only once on the transfer material (paper), this condition can be usually associated with the magnetic sleeve roller which cannot hold charge and therefore cannot establish the "memory" pattern. It is often possible to measure the distance between the ghost image to determine which component makes the largest contribution to this undesirable imaging issue. However, the actual electrostatic printer or copy machine characteristics, the toner "flowability," toner triboelectric charge properties as well as exponential memory decay times are all related to the "ghosting" phenomena.
Organo silanes and siloxanes have been disclosed in the prior art for various purposes in the field of electrophotography.
U.S. Pat. No. 5,604,039 discloses improved release agents which can be used at elevated temperatures without producing insoluble or undesirable products by gellation. The invention therein provides for a blend of non-phenol-functionalized poly(organosiloxane) fluid and phenol-functionalized poly(organosiloxane) fluid. The fluid is used as a release agent applied to the surface of the fuser member for fusing toner images to the receiving (paper). Octamethyl cyclotetrasiloxane (OCTS) is disclosed as a starting material therein.
U.S. Pat. No. 5,463,453 discloses a wet-type development unit which:
A) uses a carrier liquid composed of petroleum based and silicon based oils and B) toner particles composed of a coloring agent and binder resin dispersed in the carrier liquid. Cyclic dimethyl polysiloxanes inclusive of OCTS are disclosed as useful therein.
U.S. Pat. No. 5,233,008 discloses toner fusing members with an outer layer comprising a melamine-cured polyurethane coating, with increased solvent and thermal resistance. The polyurethane may be obtained from a combination of various starting materials, which may include OCTS.
U.S. Pat. No. 5,464,722 and U.S. Pat. No. 5,447,815 disclose the manufacture of toners and the use of silicone oils and varnishes lor treating toner additives, such as hydrophobic silica fine powder.
However, none of the above-described prior art discloses or suggests the use of dimethyl cyclopolysiloxanes, such as OCTS, against ghosting.
The present invention describes toner composition(s), which are specifically formulated to avoid ghost images, which are likely associated with the magnetic sleeve roller assembly. Although the root cause of the phenomenon is not fully understood, as these ghost images appear, this is an undesirable phenomenon.